由y=f(x) =(a-x)/(x-a-1)反解得：x=a+1- 1/(y+1),故f(x)的反函数为y=a+1- 1/(x+1),f(x)的对称中心为（-1,a+1),所以a+1=3,于是a=2.由(2-x)/(x-3)>0得不等式解集为{x|2